Abstract: The invention concerns a means for saving energy in a hydraulic circuit where pressurized oil supplied by a hydraulic pump is used to activate various functions by the aid of one or several valves (2,3,4) controlling the function. Such a hydraulic circuit is especially suitable for use in agricultural tractors, where the pressurized oil comes from a hydraulic pump driven by the engine. In conventional hydraulic circuits, a drawback is that the pressurized oil is directed through a pressure regulating valve, thereby causing unnecessary waste of energy and a need to cool the oil.

Abstract: Gear pump and motor apparatus adapted to operate both as a pump and as a motor include two meshing gears whose shafts are supported in a housing chamber by respective bearing sleeves whose end faces sealingly engage the end faces of the respective gears. An oil supply passage is formed in each of the bearing sleeves in a region diametrically opposed to flat surface portions formed on the outer peripheral surface of the bearing sleeves and near a central plane which passes through the axes of cylindrical chamber portions in which the gears are situated. Oil leaking from the pump/motor chamber is directed into spaces defined between the peripheral surfaces of the bearing sleeves and the respective chamber portions through the oil supply passages into the bearing sleeve openings to lubricate the gear shafts which are received therein. The ratio of the length to the diameter of each of the oil supply passages is less than or equal to about 10.